OSX 10.5 and 10.6 have introduced some significant changes to printer driver settings which may cause your prints to be darker than you expect when using ICC profiles.

First make sure that you are creating V2 ICC profiles rather than V4 ICC profiles as certain third party software applications may not be compatible with that platform at this time. Here is a link that will walk you through making these changes in the ColorMunki application, most of the X-Rite software programs have this set in the preferences: